This invention relates to filter systems and, more particularly, to an improved filter which provides good seeability (i.e., allows good-seeing, by a human observer with normal color vision) while simultaneously limiting the total radiation energy which impinges upon the eye.
Heretofore, little has been known about which wavelength bands reaching the eye are important to good-seeing, and which wavelength bands are either detrimental or of little use. Therefore, "sunglasses" are generally made so as to reduce the intensity of all of the different wavelength bands in the light reaching the eye. It is generally believed, however, that overall reduction of intensity of light reaching the eye always results in poorer seeing.
In U.S. Pat. No. 3,877,797 to W. A. Thornton, the present applicant, is described an optical filter combination which improves color discrimination. In U.S. Pat. No. 4,176,299 to W. A. Thornton is disclosed a method and apparatus wherein good color rendering of illuminated objects is obtained using illumination composed of only three selected wavelengths peaked at about 450 nm, 530 nm and 610 nm. This development has lead to much further work relating to the three-band response of the human visual system.